ABSTRACT Overdose acetaminophen (APAP)-induced liver injury (AILI) accounts for nearly 50% of the acute liver failure cases each year. N-acetylcysteine (NAC) is the only antidote used clinically to ameliorate AILI; however, the effectiveness of NAC declines rapidly after APAP ingestion. Developing new life-saving treatment is critically needed. APAP-induced hepatocyte stress/damage results in the activation of liver resident M?s (Kupffer cells, KCs) and the recruitment of infiltrating M?s (IMs). We and others have demonstrated a hepato-protective function of hepatic M?s. A major goal of our research is to understand the underlying molecular mechanisms. APAP challenge causes profound liver tissue hypoxia, which triggers the stabilization of hypoxia-inducible factor (HIF)1? and HIF2?. Our preliminary studies using mice with myeloid-specific deletion of HIF2? (HIF2?mye/-) revealed a critical hepato-protective function of hepatic M?-derived HIF2?. Screening of the hepatic protective and pro-toxicant factors shows that IL-6 mRNA level is significantly lower in the liver and nonparenchymal cells of HIF2?mye/- mice compared with WT mice. It is recently reported that HIF2? directly regulates IL-6 transcription. Together, these findings led to our hypothesis that APAP treatment leads to HIF2? stabilization in hepatic M?s, and that HIF2?, via promoting IL-6 production, plays a critical role in M?-mediated hepato-protection. We propose three Specific Aims to examine this hypothesis: (Aim 1). Determine the hepato-protective effect of the myeloid-specific HIF2?/IL-6 axis in AILI. (Aim 2). Evaluate the therapeutic potential of HIF stabilization in attenuating AILI. (Aim 3). Define the molecular mechanisms of the hepato-protective effects of myeloid-specific HIF2?/IL-6 axis. The findings will provide important insight into endogenous protective mechanisms during AILI. The knowledge gained could uncover therapeutic target and advance the development of antidote to treat patients with AILI.